Implantable medical devices such as implantable pacemakers and defibrillators monitor the heart's rhythm by sensing electrical signals. If a device detects an abnormal heart rhythm, or arrhythmia, it delivers therapy in the form of an electrical pulse. While such devices detect arrhythmias and take action to restore the heart's normal sinus rhythm, they can neither detect nor take corrective actions for other forms of cardiac malfunctions stemming from pathological conditions of the heart such as abnormal cardiac volume, abnormal cardiac pressure, and malfunctioning cardiac valves.
Stethoscopes have been used for many years to diagnose pathological conditions of the heart based on cardiac sounds. Examples of such cardiac sounds include the S1 and S2 heart sounds, which respectively comprise the “lub” and the “dub” of the “lub-dub” rhythm of the heart. The S1 heart sound is generated when the mitral and tricuspid valves close. The S2 heart sound is generated when the pulmonary and aortic valves close. Conditions identifiable based upon cardiac sounds comprise aortic insufficiency, atrial septal defect, coarctation of the aorta, early systolic murmur, Ebstein's Anomaly, ejection click, late systolic murmur, mitral stenosis, mitral valve prolapse, opening snap, pansystolic murmur, pulmonary stenosis, S1 splitting, S2 splitting, venous hum, ventricular septal defect, arrhythmia, valve operation, patent ductus ateriosus, etc.
The performance of the heart can also be evaluated by measuring cardiac parameters. Such cardiac parameters include cardiac volume, cardiac stroke, stroke volume, stroke flow rate, cardiac ejection fraction, cardiac pressure, and blood pressure within a blood vessel in the immediate vicinity of the heart.
There remains a need for an improved implantable medical device capable of evaluating the performance of the heart based on the relationship between the heart's electrical signals, sounds, and cardiac parameters. There also remains a need for an improved implantable medical device capable of optimizing therapy delivered to the heart based on the relationship between the heart's electrical signals, sounds, and cardiac parameters, and a method of optimizing therapy delivered to the heart based on that relationship.